1. Technical Field
The present invention relates to a line printer and a method for controlling the same.
2. Related Art
An ink jet type line printer performs printing by discharging ink from the inside of a cavity. If ink dries, the ink is thickened. There is a case in which thickened ink in the cavity causes discharge failure. If nozzle omission in which it is difficult to discharge ink from a nozzle occurs, white stripes are recorded on a recording sheet corresponding to the nozzle failure. Here, JPA-2008-284868 discloses a method for detecting nozzle omission by analyzing image data which is acquired by imaging an ink discharge state.
Since the method is a consequence management performed after the nozzle omission occurs, it is difficult to detect a symptom of the nozzle omission and to avoid image quality being deteriorated. In order to solve the problem, there has been known a method for monitoring an ink discharge state before nozzle omission occurs by applying vibration to ink in a cavity using a piezoelectric element and detecting behavior of ink with regard to residual vibration (for example, JP-A-2004-276544).
However, in the method for detecting residual vibration, a first period, in which vibration is applied to ink, and a second period, in which vibration of ink is detected as residual vibration, are necessary. In normal printing, vibration may be applied such that ink is discharged from a nozzle, and thus the second period for detecting residual vibration is not necessary. In contrast, the line printer uses a line head and performs printing by transporting a recording sheet. Therefore, if the method for detecting residual vibration is applied to the line printer, it is necessary to make a recording sheet transport speed be slow, and thus there is a problem in that the amount of printing per unit time is reduced, compared to the method for analyzing image data acquired by imaging ink discharge.